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Old 03-31-2009, 03:28 AM   #1
Mar 2009
Posts: 48
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I have been brewing with purified water for all my brewing applications, but I don't condition the water. I was wondering about the science behind Gypsum and Irish Moss. I don't use either, but see that many people do. What does it do for the water? Why is it beneficial?

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Old 03-31-2009, 03:36 AM   #2
Nov 2004
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It's not what it does for the water, it's what it does for the beer once it's in the water. Read the link below for an overview of brewing water. Irish moss is a kettle fining that helps proteins coagulate and drop out of the wort as it boils.

Water And Homebrewing

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Old 03-31-2009, 04:22 PM   #3
menschmaschine's Avatar
Jun 2007
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See BigEd's link for Ca and SO4 (gypsum is CaSO4). Some brewers add gypsum to help achieve a certain water profile (e.g., Burton) and strictly for the effect on perceived bitterness. If you were doing it for this purpose and your water has enough calcium in it for mashing and your expected mash pH is good, then you really only need to add it to the boil.

Other brewers will add it (or other calcium compounds) to decrease pH for the mash and sparge water. In this case, calcium is the primary mineral of concern. See this thread for more info on calcium.

But you should really know how much Ca and SO4 is in your water before adding any gypsum.

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Old 05-24-2009, 08:30 AM   #4
Oct 2008
Cowtown, Alberta
Posts: 65
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Also, Irish Moss doesn't affect your water - it's a fining agent that helps pull out charged particles (ie protein). You add it around 10min before the end of your boil to help hazing agents drop out, in order to improve the clarity of your beer.

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